A so-called two-component type heat-sensitive recording material using color a forming reaction between a colorless or slightly colored electron donating dye precursor and an electron accepting compound is disclosed in Japanese Patent Publication Nos. 14039/70 (corresponding to U.S. Pat. No. 3,539,375) and 4160/68 and so on. The two-component color forming type heat-sensitive recording material is prepared by dispersing a colorless or slightly colored electron donating dye precursor (hereinafter referred to as a "color former") and an electron accepting compound (hereinafter referred to as a "developer") into a fine particle state, mixing a binder and the like therewith so that these two heat-sensitive compounds are not in contact with each other and coating the mixture on a support. Particles of one or both of these heat-sensitive compounds are fused and caused to contact each other upon heating, resulting in a color forming reaction to conduct recording. Such two-component color forming type heat-sensitive recording materials are advantageous in such points that: (1) primary coloration is conducted and therefore development is unnecessary; (2) paper quality is similar to that of general paper; (3) handling is easy; (4) color density is high; and (5) upon color formation various hues can be obtained. Accordingly such recording materials are very valuable.
Recently, a heat-sensitive recording material has widely been used particularly in the field of facsimile transmissions, recorders and printers. With such increasing additional usage in the field of facsimile transmissions, facsimile recording rates have been increased. Thus, a strong demand has arisen for heat-sensitive recording materials which have a short pulse, that is, which have the ability to undergo color formation having a sufficient color density with a low heat energy input. Various approaches have accordingly been made, as disclosed in Japanese Patent Application (OPI) Nos. 18739/83, 67083/84 and 54884/85 (the term "OPI" as used herein refers to a "published unexamined Japanese Patent Application").
However, heat-sensitive recording materials which form color with such a low heat energy input have a serious problem in that they readily form color with various other impacts, that is, a chemical impact of acid substances included in a support and surface active agents added to improve surface coating properties and a physical impact of pressure and heat generated by friction, whereby fog formation takes place, resulting in largely reducing the commercial value thereof.